1. Field of the Invention
The present invention relates generally to a microphone apparatus, and is directed more particularly to a microphone apparatus for binaural sound pickup used in dummy head recording or the like.
2. Description of the Prior Art
Upon reproducing acoustic or sound information signals, the acoustic reproducing system has hitherto been variously changed from monaural system to stereo system, to four-channel system and further to multi-channel system for the purpose of providing more faithful acoustic reproduction relative to the original sound field. Further, for the above purpose, not only one microphone, but also a number of microphones have been used to establish a multi-microphone system in which the outputs thereof are properly mixed and transmitted through a required number of channels.
In these systems, however, the original sound field has to be reproduced in, for example, the listening room of a listener, and this listening room must be wide to some extent. It is noted, on the other hand, that based upon the fact that we generally use our ears to recognize the direction from which sound signals arrive and the distance from the sound sources whether they are in front or back, right or left, or upper or lower directions, it is conceived that the necessary and sufficient information transmission can be attained by producing acoustic information signals which correspond to what the two ears of a listener in the original sound field would have actually listened to. According to this idea, only a transmission system is required by which the acoustic information provided in the eardrums of the listener in the original sound field is again produced in the eardrums of the listener in the reproducing room. In this case, the reproducing room can be selected quite freely. Besides, it is sufficient if the transmission system has two channels. Such a two-channel system is very low in cost and the reproduction of acoustic information, as good as the conventional multi-channel system, becomes possible.
It is understood that experiments of a binaural stereo system along the aforesaid lines were carried out in the year 1930 by the Bell Telephone Laboratories. In this case, satisfactory reliable results were achieved on account of the performance of sound pickup microphones, reproducing headphones and the like.
There has been proposed a microphone apparatus suitable for sound pickup to satisfy the above condition. A prior art stereo microphone apparatus of this kind has a dummy head ordinarily made of silicon robber or the like, and has a pair of symmetric microphone units, each mounted at a position of the inlet to auditory canal of the dummy head or eardrum thereof. This microphone apparatus is designed so that a condition from a sound source to the inlet of the microphone may become as much as possible, close to a condition of actual human ears. However, since the size of the microphone apparatus is fixed and constant, if there is a difference between the shape and size of the dummy head and those of a listener's head, it is not always expected to achieve the sound reproduction with good results. In addition, the aforesaid microphone apparatus is expensive, and also large in volume and heavy in weight, with the result that its transportation is rather inconvenient.
In order to eliminate the aforesaid drawbacks, it has been proposed that the following microphone apparatus be used; namely, that is, the microphone apparatus comprise an arc-shaped resilient tube, a pair of microphone units attached to the opposite ends of the tube, and supporting members mounted to the pair of microphone units. Each of the supporting members serves to locate the sound inlet of the microphone to position near the orifice of the auditory canal. An output cord is led out from the center of the resilient tube, and the microphone apparatus is formed in the shape of a stethoscope.
This microphone apparatus is normally used in such a manner that it is directly mounted on human ears or located on a dummy head having no microphone. This type of microphone apparatus greatly improves the above mentioned defects, but still has the drawbacks such that it easily picks up a wind noise and is low in stability when it is mounted on the human ears.